PWM Apparatus Noise Filtering for LCD Flicker Prevention

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Solution Overview

Problem

Existing light source-driving systems for LCD panels, such as those using CCFLs and LEDs, suffer from flicker phenomena due to distorted or inconstantly generated pulse width modulation (PWM) signals caused by high frequency noise in the inverter circuit.

Innovation Solution

A pulse width modulation apparatus comprising a voltage division part, a capacitor part, operational amplifiers, and noise reduction parts that remove high frequency noise from the input DC voltage, generating a stable PWM signal by comparing divided voltages and converting them into a triangle wave signal, which is then modulated according to a dimming control signal to prevent flicker.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If PWM signal is generated using inverter circuit, then light source can be driven and brightness can be adjusted, but high frequency noise causes signal distortion and flicker phenomenon

Engineering Contradiction:

ImprovePWM signal stabilityVSAvoidhigh frequency noise

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent extracts and removes the harmful high frequency noise component from the PWM signal generation process by introducing a dedicated noise removal circuit that filters out frequencies above a predetermined threshold, separating the useful signal from the harmful noise

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent introduces an intermediary noise removal circuit between the inverter circuit and the PWM signal generation components, which acts as a mediator to eliminate high frequency noise before it distorts the PWM signal

Inventive Principle:

Principle #24Intermediary (Mediator)

2Ease of operation

If dimming control is implemented using PWM, then brightness adjustment is achieved, but noise in input DC voltage distorts the PWM signal

Engineering Contradiction:

Improvebrightness controlVSAvoidPWM signal accuracy

Core Design Contradiction:

Ease of operationVSManufacturing precision

Solution Approach 1:

The patent applies preliminary action by removing high frequency noise from the input DC voltage before it reaches the PWM signal generation circuit, preventing noise-induced distortion before it can affect the dimming control accuracy

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The noise removal circuit serves as an intermediary component that protects the PWM generation circuit from noise contamination, ensuring accurate dimming control by filtering harmful frequency components

Inventive Principle:

Principle #24Intermediary (Mediator)

3Productivity

If high frequency noise is present in input DC voltage, then inverter circuit operation is maintained, but flicker phenomenon occurs on LCD panel

Engineering Contradiction:

Improveinverter circuit operationVSAvoidflicker phenomenon

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The patent extracts and eliminates the high frequency noise component that causes flicker, allowing the inverter circuit to operate normally while preventing the harmful effect of flicker on the LCD panel

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent converts the harmful high frequency noise into a benefit by using frequency-based filtering to remove only the problematic components while preserving the useful signal components needed for normal inverter operation

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The solution stabilizes the PWM signal supply, improves product reliability, and prevents flicker phenomena on LCD panels by controlling the duty ratio of the PWM signal within a whole range, ensuring consistent light source control.

Implementation Method 1

a capacitor part charged or discharged by an input current for providing a charge voltage

Methodology Applied

Scientific EffectCapacitance: Capacitance

Implementation Method 2

a first operational amplifier operating according to a result of comparing a divided voltage output from the voltage division part with the charge voltage output from the capacitor part

Methodology Applied

Scientific EffectVoltage comparison:

Implementation Method 3

a first noise reduction part removing a high frequency noise of the divided voltage

Methodology Applied

Scientific EffectNoise filtering: Filter (electronic)

Implementation Method 4

a second operational amplifier converting a signal generated from the capacitor part into a pulse width modulation signal by a dimming control signal

Methodology Applied

Scientific EffectSignal conversion:

Data Source

PatentUS7843142B2Pulse width modulation apparatus and apparatus for driving light source having the same

Publication Date: 2010.11.30 LG INNOTEK CO LTD

AI summary

Provided are a pulse width modulation (PWM) apparatus and a light source-driving apparatus including the PWM apparatus. The PWM apparatus includes a voltage division part, a capacitor part, a first operational amplifier, a first noise reduction part, and a second operational amplifier. The voltage division part divides and outputs an input voltage. The capacitor part charged by an input current or discharged for provides a charge voltage. The first operational amplifier operates according to a result of comparing a divided voltage output from the voltage division part with the charge voltage output from the capacitor part. The first noise reduction part removes a high frequency noise of the divided voltage. The second operational amplifier converts a signal generated from the capacitor part into a pulse width modulation signal by a dimming control signal.